feat(backend): add WeatherService

Manage per-user WeatherSource instances via FeedSourceProvider,
following the same pattern as LocationService. Wire into
FeedEngineService so weather data is included in the feed.

Co-authored-by: Ona <no-reply@ona.com>

apps/aris-backend/.env.example

@@ -6,3 +6,9 @@ BETTER_AUTH_SECRET=
 
 # Base URL of the backend
 BETTER_AUTH_URL=http://localhost:3000
+
+# Apple WeatherKit credentials
+WEATHERKIT_PRIVATE_KEY=
+WEATHERKIT_KEY_ID=
+WEATHERKIT_TEAM_ID=
+WEATHERKIT_SERVICE_ID=